Introduction to SAP Paging Space
SAP systems are designed to have an optimal amount of high speed memory to handle the expected transaction load for a specified number of users. When all of this memory is being used, SAP begins writing out memory blocks that are least used to physical disk space designated as Paging space.
If you have too much paging going on then you will experience declining system performance. However, when there is not enough paging space, SAP will begin killing processes to keep the system up and running instead of allowing it to crash.
When users start telling you that they are getting dumped out of SAP or that they are getting errors that say, “MEMORY_NO_MORE_PAGING” then you are most likely running into paging space problems.
Checking the SAP System Log
To check and verify which errors are being generated, use transaction SM21 – System Log. In this case, you will probably see Overflow of Paging File errors and Short dumps as users are getting dumped. It will probably look something like this:
Overflow of Paging File (032768 Blocks) Run-time error "MEMORY_NO_MORE_PAGING" occurred > Short dump "100202 091311 sap system generated
Determining user memory allocation
You can check to see how much memory is being consumed by each user by checking transaction code SM04 – User List. Not only does it show you a list of who is on the system, but it also shows the memory consumption in megabytes for each user. You can sort the user list by the memory column to quickly identify any users that have excessive memory consumption. Typically users will consume between 1 and 50 megabytes. Rarely will you see a user go a little over that. However, if you identify a user that is consuming more than 100 megabytes it is time to look at what they are running and how they are running it.
Run away user transactions and dialog processes
Simply terminating a run away user session or cancelling a dialog process that is running wide open can resolve the paging space errors. Paging space errors can also be caused when a user is running a report in dialog mode without specifying adaquate selection criteria so that it is requesting a significant amount memory.
Training Users to run reports correctly
In this case a little user training can help resolve sporadic occurrances of paging space errors. Users should be instructed to run large reports that access excessive amounts of data in background mode instead of in a dialog session. Memory usage is handled differently depending upon what mode is being used. Of course, you may want to speak with your ABAP team to see if they can re-write a report or program that continues to be a problem so that it can run more efficiently or require more specific selection criteria.
What to look at to resolve SAP Paging Space errors
When Paging Space errors become a cronic issue you need to look at several different aspects of SAP paging space in order to determine what is causing the problem and how to resolve it.
- Physical disk space allocated to paging space
- SAP profile parameters for paging space
- Amount of physical high speed RAM memory
The correct balance of these three things will provide the optimum environment for SAP to run in and make SAP Paging Space issues a thing of the past. You may find that you need to actually increase the amount of RAM memory availble on your system.
Check physical disk space allocated as paging space
Identify how much physical disk space has been allocated to paging space at the operating system level. You might be running up against the amount of physical disk space that has been allocated to paging space at the operating system level. Make sure that SAP is not using all of the physical disk space that has been assigned to the paging file space.
The name of the SAP paging file is PAGEFIL00 and it is located in the file system /usr/sap. The full path is /usr/sap/PRD/DVEBMSG00/data/PAGFIL00
To determine if there is enough paging space available in AIX use the lsps command at the operating system level with the -a switch.
This will show you you physical paging space at the operating system level. You can see how many paging spaces are available, the physical volumes that they are set up on, the volume group, the size of each paging space and the percentage used.
If the /usr/sap file system is full you will need to get everyone off the system and bring SAP down gracefully before it comes down hard. You can then add additional space to the /usr/sap file system. You can also delete the old SAP paging space file /usr/sap/PRD/DVEBMSG00/data/PAGFIL00 and the stat* files. At this point you can bring SAP back up.
SAP Profile Parameters for paging space
The amount of paging space that is available to SAP is configured using several SAP Profile parameters. If SAP Paging Space errors is a cronic problem, you might need to increase the number of paging blocks in the SAP profile and restart the system. Look for parameters rdisp/PG_SHM and rdisp/PG_MAXFS. Remember that these parameters are set for each server. If you are using additional APP servers or DB servers, you will need to change these parameters on each one.
Additional information found in SAP notes
You can get more detailed information about SAP Paging Space by consulting SAPNotes.
SAP Note: 133909 – Maximum value for PG_MAXFS, PG_SH, ROLL_MAXFS, ROLL_SHM.